Coaxial cable is used to transmit radio frequency (RF) signals in various applications, such as connecting radio transmitters and receivers with their antennas. Coaxial cable typically includes an inner conductor, an insulating layer surrounding the inner conductor, an outer conductor surrounding the insulating layer, and a protective jacket surrounding the outer conductor.
Prior to installation, the two ends of a coaxial cable are generally terminated with a connector. Connectors can generally be classified as either field-installable connectors or factory-installed connectors. While portions of factory-installed connectors are generally soldered or welded to the conductors of the coaxial cable, field-installable connectors are generally attached to the conductors of the coaxial cable via compression delivered by a screw mechanism or a compression tool.
One difficulty with field-installable connectors, such as compression connectors or screw-together connectors, is maintaining acceptable levels of passive intermodulation (PIM). PIM in the terminal sections of a coaxial cable can result from nonlinear and insecure contact between surfaces of various components of the connector. A nonlinear contact between two or more of these surfaces can cause micro arcing or corona discharge between the surfaces, which can result in the creation of interfering RF signals.
For example, some screw-together connectors are designed such that the contact force between the connector and the outer conductor is dependent on a continuing axial holding force of threaded components of the connector. Over time, the threaded components of the connector can inadvertently separate, thus resulting in nonlinear and insecure contact between the connector and the outer conductor.
Further, even relatively secure contact between the connector and the outer conductor of the coaxial cable can be undermined as the coaxial cable is subject to stress, due to high wind or vibration for example, which can result in unacceptably high levels of PIM in terminal sections of the coaxial cable.
Where the coaxial cable is employed on a cellular communications tower, for example, unacceptably high levels of PIM in terminal sections of the coaxial cable and resulting interfering RF signals can disrupt communication between sensitive receiver and transmitter equipment on the tower and lower-powered cellular devices. Disrupted communication can result in dropped calls or severely limited data rates, for example, which can result in dissatisfied customers and customer churn.
Current attempts to solve these difficulties with field-installable connectors generally consist of employing a pre-fabricated jumper cable having a standard length and having factory-installed connectors that are soldered or welded on either end. These soldered or welded connectors generally exhibit stable PIM performance over a wider range of dynamic conditions than current field-installable connectors. These pre-fabricated jumper cables are inconvenient, however, in many applications.
For example, each particular cellular communications tower in a cellular network generally requires various custom lengths of coaxial cable, necessitating the selection of various standard-length jumper cables that is each generally longer than needed, resulting in wasted cable. Also, employing a longer length of cable than is needed results in increased insertion loss in the cable. Further, excessive cable length takes up more space on or around the tower. Moreover, it can be inconvenient for an installation technician to have several lengths of jumper cable on hand instead of a single roll of cable that can be cut to the needed length. Also, factory testing of factory-installed soldered or welded connectors for compliance with impedance matching and PIM standards often reveals a relatively high percentage of non-compliant connectors. This percentage of non-compliant, and therefore unusable, connectors can be as high as about ten percent of the connectors in some manufacturing situations. For all these reasons, employing factory-installed soldered or welded connectors on standard-length jumper cables to solve the above-noted difficulties with field-installable connectors is not an ideal solution.